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There are no absolute recognized clinical indications for the transfusion of whole blood, and therefore blood is separated into its components (red cells, platelets and plasma) prior to transfusion. Blood components can be either produced from whole-blood donations or collected directly from the donor by apheresis technology. In many countries, blood components are depleted of leukocytes prior to storage. There are several potential benefits of leukocyte depletion including reduced immune complications and transfusion transmission of some cell-associated viruses [e.g. cytomegalovirus (CMV)]; however, in the UK a perceived benefit in terms of reducing the risk of transmission of variant Creutzfeldt-Jakob disease (vCJD) was a key factor in recommending its implementation. In the developed world, the risk of blood components transmitting infection is low because of stringent donor selection and testing criteria. These risks can be reduced further by the use of pathogen inactivation systems. Systems are now licensed and in use in some European countries for pathogen inactivation of plasma and platelet components; systems for red cells are not yet available. Recently, filters designed to remove prion protein from red cells have been developed with the aim of reducing the risk of transmission of vCJD by blood, and these are under assessment in the UK. As yet, there are no filters available to remove prion protein from plasma, platelets or whole blood.